David Dowdy Profile picture
Sep 24, 2021 9 tweets 4 min read Read on X
I applaud the ACIP for taking a nuanced stance.

But am hearing lots of concern from vax'd under-65s who are worried their immunity will be gone 6 months after their 2nd shot.

To address this, let's take a tour of 2 populations of about the same size: Israel and Virginia.
First, Israel. It's essential to debunk this myth:
"Israel vax'd its population first.
It now has high COVID rates.
Vax immunity must be waning."

This storyline has a lot of problems.

First, 50% vax coverage was only achieved 6 months ago (Mar 17), 4 mos before the surge.
So when the booster was made available in Israel on July 30, only 20% of its population had been fully vax'd for 6 months.

But at the time of the Israeli surge (July-Sept), most people had not been vax'd for >6 mos.

This surge was not caused by waning immunity.
On Sept 1, 40% of Israel's population had received their 2nd dose within the last 6 months. Boosters had been available for 1 month.

Yet Israel had the highest case rate in the world that day.

All to say, this is not about waning immunity. It's about Israel being an outlier.
Also, if it were all about waning immunity, we should be seeing cases start to rise in those parts of the world (US, Western Europe) that vaccinated next.

Yet the opposite is happening (see weekly change below. Those places are exactly where cases are falling. Without boosters.
All to say, Israel is a unique context.

Now, let's go from 9 million people in the Middle East to 8.5 million in a state that voted twice for GW Bush but is now blue, and has vax + case rates similar to US median: Virginia.

Which should be more relevant to US policy?
VA has a great dashboard of cases by vax status: bit.ly/3AIiOdi

All time, unvax'd people in VA have had 8x the case rate and 7x the hospitalization rate as fully vax'd.

Most recently (week of Aug 14)? Case rate 6x higher, hosp rate 8x higher. Basically the same.
And in the most recent weeks (with incomplete data), this is not letting up. The vax is working as well now in VA as it ever has.

Since vax became available, only 927 fully vax'd Virginians have been hospitalized. In a population the size of Israel. A 1 in 5,000 chance.
All to say, if you've been fully vax'd, that vaccine is still working for you - very well.

All the more if you live in a place more like Virginia than Israel.

If you're >65 or have a weak immune system and want to get a booster, it's safe.

But otherwise, it's also OK to wait.

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More from @davidwdowdy

Jul 8, 2022
Over half of all COVID infections in the US are now BA.5.

3 reasons why this isn't as alarming as it might seem:
- Rise in BA.5 has been gradual.
- Our immune systems are better prepared.
- Places hit first by the current wave have stabilized.

Some reasons for COVID optimism:
Gradual rise:

Whereas Omicron fully established itself in 1 month, BA.5 has taken 2 months to get to 50%.

And the size of the wave has been much smaller.

Meaning that any advantage BA.5 has over other subvariants is very small, compared to the advantage Omicron had over Delta.
Viruses evolve. But our immune systems also adapt.

One can always focus on the virus for bad news. But the overall trend is good news.

Apr-June 2022 was the least deadly 3-month period since the pandemic started. Even as transmission (e.g., test positivity, orange) has risen.
Read 8 tweets
Feb 25, 2022
New COVID guidance from CDC is out:


Now setting three "community levels". Previously based on cases + test positivity, now cases + new COVID admissions + % of hosp beds occupied by COVID.

A quick hot-take🧵on pros and cons of this approach.
Pro: It uses science.

This was based on measures that most accurately predicted deaths & ICU use in 3 weeks. Far better than arbitrary goals.
Pro: Test positivity was dropped.

% of tests positive is no longer a meaningful indicator, as testing varies so widely from one location to the next, and many tests are at-home tests that are difficult to track.
Read 10 tweets
Feb 11, 2022
What will COVID look like in 2022?

Nobody knows for sure, but here's my take on the 3 most likely scenarios.

Each with reasons why that scenario might (and might not) happen.

Take home: Depends on how long & strong immunity is, w/ most people now vax'd/infected multiple times.
Scenario A: 2022 is great.

COVID levels stay very low, at least until winter. Then we boost w/ COVID + flu vax.

Why so?
- Most people now have multiple doses of immunity (vax or infection).
- Many cases could be asymptomatic.
- Europe saw this in 2020 w much less immunity.
Why not Scenario A?
- Most countries haven't gone this long w/o a wave (or very stringent restrictions).
- Immunity vs infection doesn't seem to last that long: four vax doses haven't prevented a wave in Israel.
- Betting against the virus has not been smart so far.
Read 8 tweets
Feb 3, 2022
Some students have asked me: "If I want to engage w the press in my future job, what should I learn to do?"

Here's my top 10 list of responses to this question.

Bottom line: it's not about how smart you are.

Would welcome comments on this list from my journalist colleagues!
1. Treat journalists as allies, not adversaries.

Some scientists think journalists are looking for missteps that can be misquoted.

In my experience, this is not true. Journalists want to get the story right as much as we do.

Practice interviewing as friendly conversation.
2. Do your homework.

Don't go into an interview without asking what the story is about.

Spend a few minutes making sure your numbers are right. (I often keep tabs/notes open for reference.)

Think about the 2-3 key points you want to make, so you can make them repeatedly.
Read 11 tweets
Jan 24, 2022
Now that we've been living with Omicron for 2 months, we can use this wave to learn some lessons about
COVID in general.

First: This virus likely depends on a core group of people/settings for its spread.

We can surmise this by looking at the decline of Delta.
If 1 in 3 Omicron cases is reported, the # of cases in the US now is similar to # vax'd per day in April.

Yet Delta is falling much faster today (in winter) than cases were in April.

Why? Likely Omicron (unlike vax) is infecting the people who otherwise would transmit Delta.
And Omicron-induced immunity nearly wiped out Delta - at a time when <5% of the population had been infected w Omicron.

Meaning that a small fraction of people (those most likely to get infected & transmit) and settings
(large outbreak-prone gatherings) are sustaining spread.
Read 8 tweets
Jan 18, 2022
Though guilty myself, I wish we would stop naming waves according to variant ("delta wave", "omicron wave", etc).

This makes it seem like each wave is randomly triggered by a new variant - and there's nothing we can do about it.

But in reality, we are making a lot of progress.
Each wave can be explained by a combination of behavior change, winter effect, and immunity. Without invoking variants.

And though waning immunity has played a role so far, our overall immunity is building w time. (Why the average case now is milder than early in the pandemic.)
As shown below, we were able to live more freely in 2021. Largely because of vax/immunity.

This most recent wave isn't over - and we need to act w caution until it is.

But we are not at the mercy of each new variant. Though we're all tired, things should get better soon.
Read 4 tweets

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